1. Field of the Invention
This invention generally relates to a spline bearing assembly, and in particular, to a ball spline bearing assembly which includes a plurality of balls interposed between a splined shaft and a splined cylinder which is fitted onto the shaft.
2. Description of the Prior Art
A ball spline bearing assembly is well known in the art, and it includes a shaft provided with a plurality of longitudinal inner grooves on its peripheral surface, a cylinder provided with a plurality of longitudinal outer grooves on its inner surface each opposing the corresponding one of the inner grooves thereby defining a straight passage, and a plurality of balls interposed between the shaft and the cylinder as fitted in the corresponding pair of inner and outer grooves. In such a ball spline bearing assembly, the shaft and the cylinder rotate in unison at all times however the shaft and the cylinder can move relative to each other in the longitudinal direction. For such a longitudinal relative motion to take place without limitation, the balls must be circulated in endless passages. In accordance with the prior art, a plurality of return passages are provided in the cylinder radially outward of the corresponding grooves. Such a structure requires the cylinder to be thicker and is difficult to manufacture.